The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in the present disclosure and are not admitted to be prior art by inclusion in this section.
Full dimension multiple-input-multiple-output (FD-MIMO) is a study item for the upcoming Release 12 of the third generation partnership project (3GPP) long term evolution (LTE) specifications. In FD-MIMO systems, the eNodeB (eNB) may have 16 or more different antenna elements that are configured for beamforming on one or more antenna ports to user equipment (UEs). Ideally, the throughput of the eNB in FD-MIMO systems may be expected to significantly increase with a large number of antenna elements.
However, in frequency division duplex (FDD) mode, beamforming may require channel training signals. Specifically, channel training signals may be reference signals that are sent by the eNB to each UE. The UE(s) may then respond with channel feedback based on the received channel training signals. This feedback may be used to identify the resources used to beamform one or more additional signals to the UE. Currently, the overhead associated with transmitting the channel training signals may increase linearly with the number of antenna elements. For large antenna arrays having, for example, 30 antenna elements, the overhead associated with transmitting the channel training signals may become prohibitive because the throughput gains realized through use of FD-MIMO may be offset by the overhead incurred through transmission of the channel training signals.